A. Technical Field
The present invention relates to battery-driven power regulators and, more particularly, to systems, devices, and methods for high efficiency buck-boost regulators.
B. Background of the Invention
A typical buck-boost has four switches and can be operated in various ways to regulate an output voltage that may be higher or lower than the input voltage. For example, two or four switches can be turned on and off within a single switching cycle. It is known that turning on and off all switches of the four-switch buck-boost within the same switching cycle is an inferior and less efficient method of operation. Therefore, in order to maintain high efficiency, it is desirable to activate as few switches as possible in each switching cycle, such that for the same amount of average output current the overall losses stay as low as possible. Existing four-switch buck-boost circuits are thus operated by constantly transitioning between a buck mode and a boost mode of operation, such that only two switches are active in each switching cycle rather than all four switches. However, activating two switches within the same switching cycle requires that transitions from buck mode to boost mode and vice versa be properly managed. Such buck-to-boost or boost-to-buck transitions are typically controlled in one of two ways. A first method compares the input voltage to the output voltage, whereas a second method is based on duty-cycle width. Unfortunately, both methods involve a risk of getting stuck in the wrong state when managing buck-boost transitions in existing circuits. This causes the circuit to remain in buck mode when, in fact, the input voltage is below the output voltage. Attempts to eliminate this risk typically involves providing some margins around the transition zones. However, virtually all such approaches suffer from an unwanted increase in current ripple in the transition zone itself and from a reduction in overall circuit efficiency. What is needed are tools for power regulator designers to overcome the above-described limitations.